In general, synthetic resin has been applied to a variety of industrial fields because it exhibits excellent mass productivity, moldability and durability. In particular, synthetic resin foam is light-weight and exhibits increased cushioning properties and is widely commercialized in various forms such as a protective casing for a fragile article such as a glass product, a cushioning material for packing, a tableware, consumer packaging products, food packaging products, a heat insulation material, a sound insulation material and the like.
Modern processing and packaging technology allows a wide range of liquid and solid goods to be stored, packaged, and shipped in synthetic polymeric packaging materials while being protected from harmful elements, such as gases, moisture, light, microorganisms, vermin, physical shock, crushing forces, vibration, leaking, or spilling. However, many of these materials have little, if any, functional degradability.
Due to widespread environmental concerns, there has been significant pressure on companies to develop more environmentally friendly materials. Some groups have favored the use of products such as paper or other products made from wood pulp. However, the production of paper products generally requires a tremendous amount of energy and can result in unnecessary or undesirable waste. A strong need to find new, more sustainable or renewable materials that meet necessary performance standards remains.
In view of the foregoing, much attention has been recently directed to biodegradable resins and a great effort has been made to develop biodegradable resins that can replace conventional synthetic resins. Biodegradable polymers are an alternative to petroleum-based polymers. Some biodegradable polymers degrade in only a few weeks, while the degradation of others takes several months. Biodegradable polymers are degraded by the action of naturally occurring microorganisms such as bacteria, fungi and algae. Biodegradable polymers can be made from natural polymers such as starch, sugar, or cellulose, or can be petroleum based synthetics.
Additionally, attention has been directed to making compostable polymer compositions as well as polymer compositions that are made of a renewable or sustainable material. Attention has been directed to production of polymers generated from renewable natural sources, which are often biodegradable and nontoxic. These renewable polymers can be produced from biological systems such as microorganisms, plants, and animals or can be chemically synthesized from biological materials such as sugars, starch, natural fats or oils, etc.
As a result, increased attention has been directed to processing natural polymers. However, these natural polymers are significantly more expensive to produce than their synthetic counterparts and do not exhibit the same physical properties, such as foamability, strength and heat resistance.
In particular, there have been many attempts to process starch, a natural polymer that is relatively inexpensive and is a renewable material, into a thermoplastic form to allow starch based polymers to be used in the place of non-degradable synthetic polymers. Starch has been incorporated into multi-component compositions in various forms, including as filler and binder.
Although many have attempted for years to perfect a starch composition that would yield an environmentally sound material while, at the same time, being economical to make, such a combination has not yet been achieved. Additionally, starch based polymeric compounds and products made therefrom have not met the physical properties of other non-biodegradable materials such as polystyrene.
Development of foamable blends comprising bio-based or biodegradable polymer has proven particularly difficult. Techniques of foaming synthetic resin which have been carried out in the art include a method of producing foamed beads including the steps of charging styrene beads in a forming mold and adding water vapor thereto, followed by a decrease in pressure, a method of foaming synthetic resin by charging an extruder with, for example, styrene resin together with a foaming agent such as an organic solvent or the like to foam the resin due to a pressure reducing action occurring when the resin is extruded, and the like.
Alternatively, polymer foams are commonly made using a continuous process where a blowing agent laden molten resin is extruded under pressure through an appropriate die into a lower pressure atmosphere. A batch or staged process can be used, where small polymer beads (also called particles or pellets) are impregnated with blowing agent and then expanded by heating rapidly to a temperature near or above the glass-transition or melting temperature of the polymer-blowing agent system, or subjected to an external compressive stress at a temperature up to the glass-transition or melting temperature of the polymer-blowing agent system.
However, such conventional chemical foaming techniques for foaming synthetic resin as described above fail to satisfactorily foam biodegradable resin due to a relationship between a softening point or melting point of the resin and a foaming temperature of a foaming agent and the like. Thus, there are known many problems which are encountered with techniques of foaming biodegradable resin to a high expansion and forming the foamed resin.
Therefore, a need exists for a bio-based or partially-biodegradable polymer product that is strong, not prone to mold or pests, and can be readily and inexpensively made, and preferably can be foamed to replace polystyrene foam which is not readily biodegradable.